The judge said that by not using the manufacturer's prescribed inspection technique while rebuilding an engine, the mechanic violated regulations. That seemed to imply that any manufacturer SB or instruction for doing something required by regulation took on the force of regulation itself.

Not so, said the FAA's Assistant Chief Counsel for Regulations Rebecca MacPherson.

She issued an "interpretation" of the regulations to answer a question raised by the Cessna Pilot Association's Mike Busch almost a year ago. (It appears the FAA was looking for a case to be able to clarify its position again after the NTSB decision.)

Busch asked if the regulations required a mechanic to perform a borescope inspection in addition to a pressure check of Teledyne Continental Motor (TCM) engine cylinders. That's what a TCM SB requires for 100-hour inspections.

She said no.

All that's required is that mechanics use "methods, techniques, and practices acceptable to the administrator."

Manufacturers can't issue 'substantive rules'

If manufacturers could make SBs mandatory, it would, "effectively authorize manufacturers to issue 'substantive rules,' as that term is used in the Administrative Procedures Act," MacPherson said.

But the FAA can't delegate rulemaking authority to manufacturers, and "substantive rules" must go through public notice-and-comment procedures required by law - and manufacturers can't do that.

SBs not mandatory for most AOPA members

Bottom line, if a manufacturer wants to require an owner to do something with his aircraft, the FAA has to approve it.

For most of the aircraft flown by AOPA members in noncommercial operations, the only thing you have to do is comply with the FAA's regulations and any applicable airworthiness directives (ADs).

A manufacturer's SB isn't mandatory. But check with your mechanic. Complying with an SB still might be a good idea. (And SBs sometimes become mandatory ADs after they've gone through the rulemaking process.)

The caveats: Most commercial operators do have to comply with SBs because it is required in their operations specifications.

For newer aircraft certificated under Part 23 (rather than CAR 3), SBs can be made mandatory if approved by the FAA and incorporated into the airworthiness limitations section of the aircraft's maintenance manual or instructions for continued airworthiness.